Warm up the milk (not hot to touch), add the yeast, and give it a good stir to dissolve.
Leave to rest for 1 minute.
Sift the flour in a large bowl, add the sugar, salt, butter and one egg, then pour over the yeast mixture.
Knead everything together to get a smooth elastic dough does not stick to the hands - you might need to add more flour - up to 25-50 grams more.
Cover the bowl with clingfilm, and leave to prove in a warm place for 2 hours, or until the dough is double in size.
Divide the dough into 3 parts, and roll each part into a sausage, then plait them together.
Butter and flour a tin loaf, place the plaited brioche in, and leave to prove in a very low oven for 30 minutes - my oven's lowest temperature is 30 degrees Celsius (86 degrees Fahrenheit).
Remove the tin from the oven, brush with beaten egg, then turn the temperature up to 180 degrees Celsius (360 Fahrenheit).
Bake on the middle rack for 20 minutes until the top is golden brown.
Remove from the oven, and leave to cool. To remove from the tin, run a sharp knife around the edges, it should come out easily.